1. Field of the Invention
The present invention relates to apparatus for handling glass sheets during shaping and cooling, and in particular, to a ring-like member or shuttle having an outline supporting surface that conforms in elevation to the elevational shape of a bent glass sheet supported thereon and in outline to a shape slightly inside the periphery of a bent glass sheet supported thereon. The purpose of the ring-like member is to support the glass sheet while conveying the latter in a downstream direction from a first station, usually a glass sheet shaping station, to a second station which is usually a transfer station. The transfer station is at the downstream end portion of a cooling area. After the glass sheets are shaped at the first station, the ring-like member transfers the glass sheet into a cooling area to the second station. At the second or transfer station, a plurality of rolls rise in unison to support the shaped and cooled glass sheet above the ring-like member and rotate to convey the latter from the ring-like member to a downstream conveyor which removes the glass sheet from the transfer station for further processing. The ring-like member is shuttled back to the first station to receive another glass sheet.
Initially, when a ring-like member was shuttled to transfer a glass sheet from a shaping station through a cooling area to a transfer station, a continuous closed ring was used. The closed ring had to remain in position at the transfer station until the entire length of the glass sheet after its transfer from the ring-like member to the rolls was removed to a position entirely downstream of the second position and the rolls of the vertically movable transfer conveyor section lowered to provide clearance for the closed ring-like member to be shuttled back to the first station to receive the next glass sheet undergoing processing.
In an effort to accelerate the rate of glass sheet production, the downstream end portion of the ring-like member was modified to provide a pair of downstream end portions that extend transversely toward one another in opposite transverse directions to provide a transversely extending space between the lateral inner ends of the downstream end portions. This space was of a width sufficient to provide clearance for the arrays of rolls mounted on common shafts so that the rolls could remain in an elevated position to move the lifted glass sheets downstream of the second or transfer station while the ring-like member shuttled upstream to be in position to receive the next glass sheet. Unfortunately, since it was necessary to have several rolls mounted on several shafts spaced longitudinally of the conveyor path traversed by the shuttling ring-like member, and it was also necessary for each of the shafts to support a plurality of transversely spaced rolls to insure that the glass sheet was lifted from the ring-like member in nontilting relation by having rolls disposed on opposite sides of the center of gravity of the lifted glass sheet, the clearance space occupied a considerable portion of the transverse dimension of the downstream end portion of the member. Consequently, the portion of a glass sheet unsupported over the transverse clearance space sagged uncontrollably because of lack of local support during its transfer from the first station to the second station.
Prior to the present invention, the only solution that appeared to be available to resolve the problem of uncontrolled sag in the leading edge portion of glass sheets transferred on ring-like members having a transversely extending space between the inner ends of the transversely extending downstream end portions was to return to the continuous ring construction of the downstream end portions of the earlier ring-like members that formed a continuous enclosed ring. The return to the original continuous ring construction for the shuttle member has reduced the leading edge sag in the glass sheets, but at the expense of a slowdown to the earlier rate of production because of the need for the transfer ring to await clearance of the glass sheet and lowering of the transfer rolls prior to it being free to return to the first station.
It would be beneficial to the glass sheet shaping art if the ring-like transfer member used as a shuttle to transfer glass sheets from a first station where the glass is shaped to a second station where the glass sheet is transferred from a cooling area to a downstream conveyor were able to return to the first station more rapidly than is possible with continuous ring-like shuttle members to receive a subsequent glass sheet without losing control over the shape of the glass at its leading edge portion.
2. Description of Patents of Interest
U.S. Pat. No. 4,092,141 to Robert G. Frank and DeWitt W. Lampman provides a method and apparatus for conveying glass sheets through a furnace on conveyor means, heating the glass sheets while passing through a furnace to a temperature approaching the glass softening point. At a shaping station beyond the furnace, each glass sheet in turn is lifted into engagement with an upper vacuum mold having a shape conforming to that desired for the glass sheet. The upper vacuum mold remains at the shaping station and holds the shaped glass sheet thereagainst as the lifting means retracts to below the level of the conveyor means. A continuous ring member shaped to support the bent glass sheet adjacent its marginal or peripheral edge only, moves generally horizontally as a shuttle between the shaping station and through a cooling area to a transfer station to receive each shaped glass sheet released by vacuum to deposit the sheet onto the tempering ring at the shaping station and transfer it through the cooling area to the transfer station.
After the sheet is shaped and cooled, a vertically movable sheet transfer means rapidly lifts each bent glass sheet to remove the latter from the continuous ring member after the glass sheet has had its surfaces hardened sufficiently to permit it to be conveyed on an additional downstream conveyor providing spaced rotating rolls along a glass sheet supporting surface at an elevation slightly higher than the level at which the glass sheet is supported by the continuous ring member. However, since the transfer and continuous ring member is endless, the apparatus of this patent delays the return movement of the continuous ring member to the first or shaping station until after the trailing edge of the shaped, surface hardened glass sheet has moved downstream into a position in which the entire glass sheet is completely beyond the transfer and tempering ring, and the transfer means is lowered to a position providing clearance for returning the shuttling continuous ring member to the first station.
The sheet transfer means for removing the glass from the tempering ring to the additional downstream conveyor according to the Frank and Lampman patent comprises a frame support and lifting and lowering mechanism for raising and lowering the frame support and a plurality of rotating conveyor rolls having doughnut shaped support members carried by narrow shafts mounted on the frame support. The apparatus is so constructed that the conveyor rolls of the sheet transfer means are arranged in a matrix on parallel shafts that move vertically in unison between a lower, recessed position where the rotating conveyor rolls are clearly below the movement of the continuous ring member and its supporting carriage and a raised position wherein the rotating conveyor rolls have a common upper tangential surface and provide rotating elements of a glass sheet supporting surface disposed above the level of support provided by the upper edge surface of the continuous ring member and at a level of support provided by a tangential surface common to the rolls of the additional downstream conveyor.
U.S. Pat. No. 4,185,986 to Robert G. Frank provides a feature that enables a ring-like member, which is substituted for the continuous ring member of the previous patent to start its return to the shaping station sooner than permitted by the prior art and, more specifically, before the vertically movable rotating conveyor rolls of the glass sheet transfer means have moved the tempered glass sheet beyond the extreme downstream position that the ring-like member occupies during the production cycle and before the rotating rolls of the sheet transfer means are lowered to their recessed position. The ring-like member of the latter patent comprises a pair of downstream end portions which extend transversely toward one another and are laterally spaced from one another to provide a single, transversely extending space therebetween. The transversely extending space provided in this patent is slightly wider than the space between the outer surfaces of the transfer rolls mounted on common shafts to permit the vertically moveable transfer means to be entirely clear to move between the lateral inner ends of the spaced transversely extending downstream end portions of the ring-like member even when the transfer means is in its raised position. Unfortunately, in dealing with glass sheets of 1/8 inch thickness (3.2 mm.) and less, the time needed to transfer a hot glass sheet from the shaping station to the transfer station was such that the unsupported leading edge portion of the glass sheet in the downstream end portion of the glass developed sag beyond tolerance limits.
The first solution to this problem was to reduce the rate of production by reinstituting the continuous ring member disclosed in the earlier Frank and Lampman patent for the ring-like member having the discontinuous downstream end portion of the later Frank patent. It would be more desirable to maintain the production rate developed by the Frank patent without continuing to have the leading edge portion of the glass sheet sag beyond limits acceptable to the customer.